05-26-2008 10:14 PM - edited 03-05-2019 11:14 PM
Hi there, i have 2 switches, a 2960 and a 3750 connected with trunk links. In the 3750 switch i have the native vlan tagging on. On 2960 i was told by cisco personnel that i doesn't support native vlan tagging. Though, i have placed a sniffer on the 3750 and i get tagged and untagged frames. Isn't it a little strange? Shouldn't the 3750 reject all the untagged frames?
05-26-2008 10:23 PM
Well. 2960 is sending the untagged frame for native vlan across the trunk and is expecting the same from 3750. once the 3750 receives the untagged frame, it will drop it and will result in a trunk port misconfiguration error.
You should enable the native vlan tagging on both the sides. You can also get away with this by using a bogus vlan as a native vlan on the trunk ports. This way all the user data vlans will be tagged across the trunk link.
-amit singh
05-26-2008 10:27 PM
Îι and thanx for the quick response. Native vlan tagging is enabled on 3750 but not on 2960 cause it doesn't support it. But i can ping from one device to the other.
05-26-2008 10:36 PM
pings during this config might/might not work but this is not a recommended config. If this condition is true then the switches will be buffering the logs. This would significantly impact the performance over the lan.
Please paste the "show log " and " show config " from both the switches.
-amit singh
05-26-2008 11:56 PM
3750 :
3750#show run
!
no aaa new-model
switch 1 provision ws-c3750g-24ts-1u
switch 2 provision ws-c3750g-24ts-1u
system mtu routing 1500
vtp mode transparent
udld aggressive
ip subnet-zero
no ip domain-lookup
!
!
spanning-tree mode rapid-pvst
no spanning-tree optimize bpdu transmission
spanning-tree extend system-id
!
vlan internal allocation policy ascending
vlan dot1q tag native
!
vlan 2
name Switch
!
interface GigabitEthernet1/0/2
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface GigabitEthernet1/0/23
description L2 Trunk Connection to switch - GigEth 0/1
switchport trunk encapsulation dot1q
switchport mode dynamic desirable
!
interface Vlan1
ip address 1.1.1.1 255.255.255.0
!
interface Vlan2
ip address 10.10.7.217 255.255.255.252
2960:
Switch#show run
!
hostname Switch
!
no aaa new-model
system mtu routing 1500
ip subnet-zero
!
!
!
!
no file verify auto
!
spanning-tree mode rapid-pvst
spanning-tree loopguard default
spanning-tree portfast default
spanning-tree extend system-id
spanning-tree vlan 2 priority 28672
!
vlan internal allocation policy ascending
!
interface Port-channel1
switchport trunk allowed vlan 2,714,717
switchport mode trunk
!
interface GigabitEthernet0/1
description trunk connection to 3750 gig1/0/23
switchport mode dynamic desirable
!
interface Vlan1
ip address 1.1.1.2 255.255.255.0
no ip route-cache
!
interface Vlan2
description Management VLAN
ip address 10.10.7.218 255.255.255.252
no ip route-cache
!
ip default-gateway 10.10.7.217
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